Astrology is the mass cultural delusion that the apparent position of the sun and planets relative to arbitrarily defined "star signs" at the time of your birth somehow affects your personality and future.[2]

According to the Faculty of Astrological Studies, astrology "explores the meaningful connection between mankind and the wider cosmos, the relationship between the movements of the planets and the inner world of human consciousness and motivation."[3] Some supporters like to emphasise that astrology is complex, and goes beyond just the simple "Sun Signs" people are used to[4] and others like to add amusing little rationales such as “Every human being contains every sign and every planet.”[5] Stripped of any fancier and woo-like terms, it is the belief that huge balls of rocks, liquids, gases, and nuclear fusion reactions billions or trillions of miles away from Earth can affect the financial, sexual, emotional, and employment situations of individual carbon-based life forms on one specific planet. Put like that, it sounds absurd, yet unlike many practitioners of alternative medicine who like to hide the absurdities behind complex terminology or assertions of mysterious energies, even fairly "advanced" astrology is still pretty open about the fact it's predicting the future based on staring into the sky.[6]

This widely believed idea has never produced any worthwhile and conclusive predictions, in spite of having several different formulations across disparate cultures. As far as astrology produces falsifiable predictions, it has been thoroughly falsified as no better than guesswork. As all the "evidence" that it is true is only anecdotal, selectively reported, or made up, it is an excellent example of a woo explanation for something quite mundane.

Because astrology is an ancient pseudoscience, its historical form can differ from the modern-day version. Indeed, there are many astrological traditions that vary from culture to culture, many associated with religions. Wide definitions of what constitutes astrology have been provided by historians and anthropologists. Patrick Curry defines astrology most broadly as:[7]

The practice of relating the heavenly bodies to lives and events on earth, and the tradition that has thus been generated.

Astrology today is the common computation and consultation system used by modern astrologers to explain personality types and factual events of today in terms of planetary movements and positions in their system. This is slightly more complicated than using birth month (which is used in horoscopes, as many people are familiar with), although it is no less accurate. Indeed, thanks to a few seasonal factors (see birth month, below) this may actually be less useful. However, it allows astrologers to sell personalised readings and give the impression that they've actually put some work into it.

From astrology — Wiktionary, astronomy — Wiktionary, and the Liddell-Scott Lexicon, both words are derived from Classical Greek ones, astrologia and astronomia, and both words were used back then for discussions of celestial entities. It is only later that "astrology" got specialized to stardivination and "astronomy" for star science. Its name thus looks much like the names of numerous reputable scientific and technical disciplines, names that end with -logy. A more appropriate name for astrology would be "astromancy", in analogy with the numerous forms of divination named with the suffix -mancy.

Professor Steve Farmer has argued in papers like Neurobiology, layered texts, and correlative cosmologies: A cross-cultural framework for premodern history that several premodern belief systems may reasonably be described as "correlative cosmologies", belief systems that associate members of various sets of entities and events with each other, like celestial and terrestrial ones. He notes that in the West, they reached their height in the Renaissance, but soon went into decline. He describes his paper, coauthored with John B. Henderson and Michael Witzel, as "The first published paper to seriously link neurobiology and the evolution of religious and philosophical traditions, in a cross-cultural study of so-called correlative systems (in China), bandhus or upanishads (in India), and systems of correspondence (in the West)."

Astrology is an obvious example of a correlative cosmology. Astrology is based on correlations of celestial and terrestrial entities and events. Some of these have been worked out in incredibly gory detail by various astrologers. Renaissance Astrology has a collection of some writings of medieval and early-modern Western astrologers like Al Biruni and William Lilly, writings where one can find some of these correlations. Looking elsewhere, the medieval Western doctrine of signatures states that medicinal plants resemble parts of the body that they most useful for. Thus, liverwort got its name because its resemblance to livers suggested that it would be good for liver diseases. Meanwhile, in China, the Wu Xing was developed. It is variously described as the Five Elements, the Five Phases, the Five Agents, the Five Movements, the Five Processes, and the Five Stages. It is a correspondence of sets of five of materials, elements, planets, cardinal directions, colors, shapes, seasons, etc. Astrology is thus the main survivor of a lost world of woo-woo.

A person's sign is supposed to be whichever constellation the Sun was in when they were born. However, it almost never is; only if your birthday is near the end of a specific range might that constellation actually be right. There are two reasons that the typical dates are inaccurate.

Constellations have different sizes: each sign occupies the dates for a thirty degree range along the ecliptic, the path the sign appears to travel. This is at odds with reality, where each constellation has varying size and is never exactly 30° along the ecliptic. It means that constellations that barely touch the ecliptic, like Scorpio, get a 30-day range just because they happen to lie on one of the 30° increments. It also results in Ophiuchus, which is is larger than and takes up almost twice as much space on the ecliptic than Scorpio, getting completely skipped.

Earth's axis precesses: the typical dates have stayed exactly the same over thousands of years, even though the seasons and solstices have been gradually shifting over that time. The end result is that, while the Sun might have been in Capricorn during the beginning of January in the past, January has since moved to start when the Sun is in Sagittarius.

Since it's still fun to pretend, you might want to know what your actual arbitrary constellation is. Using the IAU-defined constellation boundaries, the current dates are:[8]

Constellation

Usual dates

Actual dates

Aries

21 March – 20 April

19 April – 13 May (25 days)

Taurus

21 April – 21 May

14 May – 19 June (37 days)

Gemini

22 May – 21 June

20 June – 20 July (31 days)

Cancer

22 June – 22 July

21 July – 9 August (20 days)

Leo

23 July – 22 August

10 August – 15 September (37 days)

Virgo

23 August – 23 September

16 September – 30 October (45 days)

Libra

24 September – 23 October

31 October – 22 November (23 days)

Scorpio

24 October – 22 November

23 November – 29 November (7 days)

Ophiuchus

N/A

30 November – 17 December (18 days)

Sagittarius

23 November – 21 December

18 December – 18 January (32 days)

Capricorn

22 December – 20 January

19 January – 15 February (28 days)

Aquarius

21 January – 19 February

16 February – 11 March (24 days)

Pisces

20 February – 20 March

12 March – 18 April (38 days)

Note that the dates for Libra and Scorpio do not overlap at all; anyone who thinks they are one of those is definitely something else.

When defending this discrepancy, astrologers claim that signs and constellations are two different things. Indeed, the modern tropical zodiac was created by taking the equinoxes and solstices and corresponding them to the four "cardinal" signs, and finding the rest of the signs by dividing the four seasons into three signs for a grand total of 12. The modern Western zodiac has little to do with the constellations its 12 signs are named after, and more to do with the sun's cycle between the Tropic of Cancer and the Tropic of Capricorn.[note 1] It's not technically astrology, it's season-ology.

That being said, Vedic Astrology is sidereal, meaning that is based on where the constellations are now rather than where they were in antiquity the way Western, or tropical astrology is. They still, however, do not use Ophiuchus. Because again, this stuff is arbitrary.

The scientific view, in the most candid form, is that astrology is a load of ancient nonsense that is, these days, perpetrated by ignorant fools or those wishing to exploit others. It is, for lack of a better word, crap. In the interest of being factual, honest, and accurate rather than merely rhetorical, the scientific point of view will be spread out in more detail below, but it will come to the same conclusion: astrology is crap.

Some of the celestial objects that supposedly rule our lives as seen through the Hubble Space Telescope

Fundamentally, astrology is the assertion that stuff happening in space affects us here — astrologers may suggest that it allows for predictions, but such predictions would not be possible if a connection did not somehow exist. This section explores whether such forces could exist. Astrologers may claim straw man here, but if there was a theoretically possible way to determine future events (or dictate personality types) there would be some connection whether they like it or not.

There is no known mechanism whereby a person could be significantly influenced by distant celestial bodies. A psychological explanation - where pretty shapes in the sky sub-consciously alter people's moods, perceptions or desires, like an accidental form of advertising or brainwashing — is unlikely as stars and celestial objects don't tend to be visible during the day and, with the exception of very dramatic events such as eclipses, all look the same to the untrained eye. In addition, viewing the stars (in order to be psychologically influenced by them) isn't a prerequisite for astrology, as a predictive mechanism, working.

More "physical" explanations are equally unlikely — this requires briefly looking into the physics that could possibly be behind it. The fundamental natural forces in nature are the strong and weak nuclear forces, the electromagnetic force, and the gravitational force. The strong and weak forces are nuclear forces, and are not applicable to interactions between people and objects such as planets or stars — their strengths tail off so dramatically that they barely have any effect outside the nucleus of an atom, let alone at the macroscopic scale. Similarly, the electrostatic force — while acting at greater distances than nuclear forces — becomes completely negligible at modest distance, and does not act in any way over astronomical distance.

This leaves us with the one remaining "long distance" force; gravity. However, despite working over far vaster distances than other forces, it is still practically impossible for planets to influence actions on Earth. Gravity follows the inverse square law, that is, that gravitational strength is proportional to the inverse of the square of the distance. As distance increases, gravitational pull decreases very dramatically; something that moves to twice as far away exerts a quarter of the gravitational pull, something three times further away exerts a ninth of the gravitational pull. Newton's law of gravitation can be used to show that, at its closest approach to Earth, the planet Mars exerts approximately the same gravitational force on a person as a 50-ton fully-loaded big rig placed 15 yards from that same person. The star Alpha Centauri A has a mass of 1.1 solar masses and is one of the three stars closest to Earth, yet its gravitational pull on a person is comparable to that of a 100-gram cellphone at 9 meters. The moon and sun, being closer, exert more force on the earth and result in the changing of tides (although this system is a little more complex than "the moon pulls water towards it"). Astrology is often not limited to just these two objects with the highest degree of gravitational interference and even so, these should — like with water in the tides — affect everyone equally.[9]

The great distances of these objects produce a further problem. Their pull on us is very close to their pull on the Earth as a whole. This differential pull is the tidal force, and it goes as the inverse cube of the distance. Not surprisingly, tidal forces are even smaller than overall gravitational ones. The planet Mars produces as much tidal effect on us as a small sand grain (diameter: 0.1 millimeters) at 1 yard or meter, and Alpha Centauri as much as a small virus (diameter: 30 nanometers) at that distance.

Astrological forces, furthermore, are allegedly powerful enough that they cannot be escaped by shielding or descent underground. It is possible to evade electromagnetic radiation of all kinds. Although it is possible to protect oneself from electromagnetic radiation (radio waves, infrared and ultraviolet radiation, visible light, X-rays) and ionizing radiation by shielding or going underground, astrological 'forces' supposedly can pass through lead-lined shielding or several meters of rock or hundreds of meters of water — the latter not creating its own astrological effects. Going into a mine, tunnel, cave, or submarine in an effort to avoid 'unfavorable' influences in one's horoscope gives one no protection (not that mines, tunnels, caves, and submarines are without their own dangers).

Whatever the mysterious force may be that astrologists claim causes the effects of the positions and movements of celestial bodies on human physiology, it is not backed up by any current knowledge or research and certainly isn't real. If there is a force, it can't be detected, and woo pushers tend to like that sort of thing — but this raises an important question; if it can't be detected in any way, shape or form, then how can it actually affect anything? However, we can still be open to so-called "supernatural" explanations and only look at the efficacy of astrology, treating it as a purely empirical question.

One force that almost certainly has an effect on people is the month they were born — though this has nothing to do with sun or star signs. Research in Queensland University showed that in the Australian Football League (AFL) there were 33% more players born in January and 25% fewer in December.[10] A sign that the solar cycles can affect your sports playing ability? Not at all; it's simply a case of when the Australian school year begins. Those born in January are nearly 12 months older than peers born in the following December, but are placed in the same school year — and the older ones are at a significant advantage at sports. When replicated in other countries with different distributions for the school year, the months where this trend appears shift accordingly.[11] This at least highlights some of the (very naturalistic) effects that need to be controlled for when assessing things like astrology; it is almost trivial to guess some trends but misread what causes them. In this case, the relative age effect is shown to have a cultural and location dependence, which would not be consistent with astrological predictions based on stars. The complexities involved in seasonal cycles to weather patterns, sunspots and food production, mean that time and date almost certainly correlate with a multitude of factors that can appear as very real trends. The development of astrology may have been tapping into these observations, but then overextended the effect to things that were just plain wrong. What is certain, however, is that attributing these simple correlations to quasi-magical forces and star signs is wrong.[12]

Assuming astrology does work, then we should be able to get a reliable definition of what "astrology works" means. In this case, it should provide a reliable source of accurate predictions and statements, and these should be better than randomly guessing once naturalistic explanations for any successes (or in less politically correct terms, cheating) has been controlled for. This is an important aspect of testing astrology, as practitioners are highly likely to worm out of such conditions.[13] The American Federation of Astrologers suggest that astrology is "all in the timing"[14] which can be read as a tacit admission that a prediction that happens to be wrong was just badly timed, and therefore shouldn't count. One of the great successes of woo movements is convincing people that it's legitimate to ignore such misses, and to think that a technique works except for the times that it doesn't. As a very good "technique works except for the times that it doesn't" is perfectly naturalistic guesswork, then holding up astrology to this standard is a perfectly valid way — indeed, it is the valid way — of testing its veracity.

Simple tests of horoscopes can be made by cutting the predictions and scrambling what signs they refer to — or perhaps asking astrologers and/or amateurs to match the description with the sign. As people happily read what they like into statements as vague as horoscopes, this never ends in astrology's favour.[15] A test titled "A Scientific Inquiry into the Validity of Astrology"[16] had this to say in its abstract, demonstrating a fairly easy test protocol that should differentiate astrology being reliable and being bullshit:

Six expert astrologers independently attempted to match 23 astrological birth charts to the corresponding case files of 4 male and 19 female volunteers. Case files contained information on the volunteers' life histories, full-face and profile photographs, and test profiles from the Strong-Campbell Vocational Interest Blank and the Cattell 16-P.F. Personality Inventory. Astrologers did no better than chance or than a nonastrologer control subject at matching the birth charts to the personal data; this result was independent of astrologers' confidence ratings for their predicted matches. Astrologers also failed to agree with one another's predictions.

While astrologers and believers may accuse science of being quite dogmatic over the "astrology is bullshit" line, rest assured it has been tested. If astrology was anywhere near as potent a tool as believers and astrologers suggest, results from even small-scale tests should end positively. One of the more famous and better controlled studies is the one performed by Shawn Carlson and published in Nature in 1985.[17][18] Here astrology was "given every reasonable chance to succeed", according to the author, but it failed. Astrologers were given the task of matching birth charts to personality types — a fairly simple task for a discipline that claims that your birth chart is "as unique as you are" and "reveals your potential in this lifetime and also where you are in that journey". Indeed, what would those phrases even mean if such a task couldn't be performed by an expert astrologer. However, astrologers themselves weren't best pleased with such a negative result, citing various issues with the apparently simple test. An article in the Astrology News Service is a curious example of kettle logic as it seems to simultaneously assert that the test was unfair and skewed, and so unlikely to show any effect, and that reanalysis of the data suggests the astrologers were correct[19]

At the beginning of 1610, Galileo Galilei looked at Jupiter with his telescope. The planet was resolved as a disk, and it had three faint stars nearby. A day or so later, he looked again, and the stars had moved. He continued to observe the planet, and he noticed that these three stars, and a fourth one also, were moving back and forth relative to Jupiter. He concluded that here were four objects that orbit Jupiter. The next year, a certain Francesco Sizzi of Florence made an astrological sort of argument that those moons cannot possibly exist. He wrote Dianoia astronomica, optica, physica, qua Syderei Nuncij rumor de quatuor planetis à Galilaeo Galilaeo mathematico celeberrimo recens perspicillì cuiusdam ope conspectis, vanus redditur. Auctore Francisco Sitio Florentino (in Latin; lpetrich's translation of its title: "Understanding of astronomy, optics, and physics, about a rumor in Sidereus Nuncius about the four planets seen by the very celebrated mathematician Galileo Galilei with his telescope, shown to be unfounded.") Here is his main argument (book page 16). In the macrocosm, there are seven planets: two favorable (beneficas) ones, two unfavorable (maleficas) ones, two luminaries, and unique Mercury, erratic and indifferent (vagum & indifferens). In the microcosm, the human head has seven openings: two nostrils, two eyes, two ears, and one mouth. He also noted that there are seven days in the week, seven metals, etc. Given all these corresponding sets of seven, there was clearly no place for the extra planets that Galileo had claimed to have discovered. So they do not exist.

Conversely one has to wonder why astrologers did not discover the existence of Uranus, Neptune, and Pluto -among other Solar System bodies not known to the developers of astrology- based on how their predictions were messed by the influences of several unknown bodies, before astronomers discovered them[note 2].

Except on a few cases as Orion, Ursa Major, or Scorpius, where some of the brightest stars that form a constellation are physically associated and at relatively similar distances to us[note 3]. Typically, said stars are at very different separations from Earth and appear to form a (more or less) recognizable pattern just from our vantage point. In addition to this, as stars -the Sun included- orbit through the Milky Way said patterns change in a scale of many thousands of years becoming distinct with time[note 4].

In addition to that, not only the twelve zodiacal constellations are the ones that are visited by the Sun, the Moon, and the planets. Ophiuchus is the best example, having been left out by the Babylonians as they had a twelve-month lunar calendar, but if one includes others the (western) Zodiac would have up to twenty-five ones[note 5].

Apart from Pluto, astrology does not take into account the dwarf planets - yet their gravity does have small pertubative effects on the orbits of other planets and the sun itself.

Predictions made by astrologers vary wildly from the vague to the specific — though most often they are extremely vague or at least vaguely in line with what most people think based on looking at the world around them, rather than the sky above. For instance, one prediction suggests "With Neptune in Pisces until 2024, we’ll see issues coming up in politics around water. There will be more flooding than ever before, unexpected hurricanes, tornadoes, typhoons and storms and towns and cities will disappear in the twinkling of an eye"[20] — which most climatologists suggest may well occur due to global warming. Indeed, other items mentioned in that prediction include "more products using nanotechnology", as if the increased use of a scientific buzzword was somehow only predictable through reading the stars and "expect to see huge growth in digital information clouds. At some point we’ll be able to stream all our music, TV, movies and books through subscription services. We’ll start to connect in new ways and we’ll know much more about each other" is bordering on self parody.

Generally, the more vague a prediction, the higher the chance it has of coming true. More accurately, the higher the chance that it can be interpreted as having been true after the fact, or retroactively reinterpreted as having not occurred because of some good graces. This can be seen most easily in the form of astrology that most people are familiar with; the horoscope. A horoscope is a prediction or advice based only on someone's date of birth, or more commonly (in newspapers and magazines, for instance) their zodiac sign, of which there are 12. Given that there are more than 6 billion people on Earth, at least one horoscope in every publication applies to more than 500 million people from the pigeonhole principle.[note 6] This gives more than enough room for even specific predictions to come true for a large number of people purely by accident. It is a clear fact that half a billion people do not have the same experiences each day, so the power of these predictions cannot be as widely and universally applied as is claimed.

Another trick used by astrologers is to give information that almost sounds like a contradiction. For example "You are an independent thinker who values the insight of others", or "You stay true to your plans but are very adaptable". If you are a Capricorn (an introverted sign) but you have a Leo moon (very extroverted), you can relate to one or the other depending on whether you feel more extroverted or introverted. People are incredibly complex, so throwing out more adjectives for every planet position will certainly make people think that their birth charts mean anything. If they disagree with any of the adjectives, the astrologer will simply say that a certain aspect of their chart causes them to differ.

The Forer effect is where an over-generalised reading can be interpreted as very accurate by many people simultaneously. Often, Forer-type readings are very flattering or complimentary, but they can also mention hidden criticisms and insecurities that people realise they experience, but might not attribute to others and certainly like to hide. Therefore, by including statements like "you try to be bold, but worry about what other people might think of your actions and hesitate" you can give the impression you really did figure out new knowledge.

James Randi once replicated an experiment to demonstrate how people can basically be "tricked" into thinking a horoscope is accurate. A number of students were asked their zodiac and given the appropriate horoscope to read. They were then asked to grade how accurate they felt the horoscope was regarding their selves and a significant number, if not the majority, gave their horoscopes scores ranging from 4 to 5 (the maximum). Later they were asked to pass along their personal horoscope to the person behind them where the "trick" was revealed; they had all been given the same horoscope.[note 7] This is a demonstration of the Forer effect and how the language used in horoscopes can be vague and widely applicable to many people yet still give the illusion of being very specific. With a careful selection of language, phrases and tone, it is almost impossible for a horoscope to not to be applicable to someone.[21]

Like many protosciences, astrology provided the original foundation of a modern science, in its case astronomy. As scientists started trying to understand what the bright things we see in the sky are, where they are, and their relationship to each other, astrology was able to provide some thousands of years of observations to develop hypotheses from. After all, mystics spent so much time gazing at the sky that it was inevitable some useful information would slip into human knowledge.

To a lesser extent, horoscopes - which would include fairly accurate astronomical data - of figures in the past and clear mentions of what were then "astrological" events may help modern historians with efforts to assign accurate dates to the past.

Whatever you do, however, do NOT confuse astrology with astronomy when talking to an astronomer—you will be soundly rebutted and possibly insulted. Even Chuck Norris wouldn't dare to mix up the two professions.

The earth rotates on an axis tilted about 23.4° in position to the sun; the exact direction of the tilt slowly rotates over time, and it takes about 26,000 years to complete one round. This is called Axial precession. Astrologers maintain that there are twelve 2,160 year "ages"; one for each sign of the zodiac (26,000 ÷ 12 = 2,160).

According to the astrologers, the change from one age to the other can cause the rise and fall of civilizations, cultural changes, and all sorts of shit. There is disagreement among astrologers over whether this "age" has already started, or is forthcoming.

For example David Williams claimed that the Age of Aquarius started in 1844 and attributes the rise of socialism, communism, and fascism to it [23] and Marcia Moore & Mark Douglas credit the American Revolution, the Industrial Revolution, and the discovery of electricity to it.[24] There are about as many variants as astrologers, as it's all simply asserted with no empirical evidence.

Some have interoperated astrology and 2012 apocalypse theories and claimed that Age of Aquarius will occur in 2012, leading to all sorts of spectacular good shit such as free energy and "spiritual growth".[25][26] Well, it seems they were as wrong as the doomsayers...

“”What utter madness in these astrologers, in considering the effect of the vast, slow movements and change in the heavens, to assume that wind and rain have no effect at birth!

—Marcus Tullius Cicero, 44 B.C.E

“”I don't know how many of you people believe in astrology.... (Girl in audience: You're a Sagittarius!) Yes that's right, that's right baby... (I love you.) I'm a Sagittarius. (I know. I read up on you....) The most philosophical of all the signs. (So am I.) But anyway, I don't believe in it. (I don't either) I think it's a bunch of bullshit, myself. But I tell you this man...I don't know what's gonna happen, man, but I'm gonna have my kicks before all the whole shithouse goes up in flames.

—Jim Morrison

“”Now you may find it inconceivable or at the very least a bit unlikely that the relative position of the planets and the stars could have a special deep significance or meaning that exclusively applies to only you, but let me give you my assurance that these forecasts and predictions are all based on solid scientific documented evidence, so you would have to be some kind of moron not to realize that every single one of them is absolutely true. Where was I?

The problem with all of this is that it gives astrologers an easy way to get out of an argument about astrology's legitimacy — "Oh, of course you don't believe! You're a _________, and they are __________."